Automatic material proportioning system



May 26, 1959 I Filed Sept. 16, 1957 AUTOMATIC MATERIAL PROPORTIONING SYSTEM A. s. HENDERSON ET AL 2,888,026

5 Sheets-Sheet 1 FTTOIPNEYS. r

May 26, 1959 A. s. HENDERSON ETAL 2,883,026

AUTOMATIC MATERIAL PROPORTIONING SYSTEM Filed Sept. 16, 1957 5 Sheets-Sheet 2 l mm m AMY May 26, 1959 A. s. HENDERSON ETAL 2,888,026

AUTOMATIC MATERIAL PROPORTIONING SYSTEM Filed Sept. 16, 1957 5 Sheets-Sheet 3 May 26, 1959 A. s. HENDERSON ET AL 2,838,026

AUTOMATIC MATERIAL PROPORTIONING SYSTEM May 26, 1959 A.-S. HENDERSON ET AL 2,888,026

AUTOMATIC MATERIAL PROPORTIONING SYSTEM I Filed Sept. 16, 1957 s Sheets-Sheet 5 IIVI/EA/Tfl/FS.

J. /t/YJEIFJON GNP/POLL 17. Cross 0w 1?. 17/505 IIZ'I'OlP/VEYS.

United Sta es AUTOMATIC MATERIAL PROPORTIONING SYSTEM I Ashland S. Henderson and Carroll D. Cross, Silver Bay,

Application September 16, 1957, Serial No. 684,117

11 Claims. (Cl. 137-88) This invention relates to novel and improved means for automatically controlling to a predetermined extent the amount of a material to be added to a second material which is moving on a conveyor, and which has constant magnetic characteristics. It is particularly adapted to the automatic control of the amount of coating material to be added to a moving mass of pellets formed from a magnetic ferrous metal ore such as beneficiated taconite.

In the induration of compacted pellets or small globules formed from beneficiated taconite powder, the pellets are heated to a high temperature in the order of 000-2400 F., usually by means of burning oil or gas jets. It has been found advantageous to coat the pellets with an adhering layer of powdered carbonaceous fuel such as coal which of course burns under the conditions above indicated, and which expedites and accentuates the induration process both from the standpoint of heat application, and chemical interaction.

Briefly, the pellets or compacts are first formed into small balls by rotating a large hollow drum on a slightly inclined cylindrical axis with the moist ore powder turning over and over on the inner drum wall as the drum rotates. The ore particles agglomerate by snowballing into spherical masses ranging in size from onequarter inch to somewhat over one inch in diameter, or possibly larger. By suitable control of the moisture, speed of rotation of the balling drum, and other factors, the production of spherical or approximately spherical balls or compacts may be satisfactorily accomplished. At this point of the operation the pellets should be strong enough to hold their shape preparatory to the heat-hardening steps.

These green or moist compacts, herein for convenience termed pellets are then coated with the aforesaid carbonaceous fuel in a coating drum by rolling them within the coating drum in the presence of the powdered carbonaceous material. The pellets and the coating powder are continuously introduced at one end of the drum and the coated pellets are discharged from the other end of the drum to a conveyor which carries them to the indurating furnace. This furnace may be of any suitable type such as the horizontal grate type or the vertical shaft type.

The procedure so far described is not an essential part of the present invention but is included here for a more intelligent understanding of pelletizing and indurating problems. A method of producing ore pellets including induration of pellets which have been coated with solid carbonaceous fuel is more fully described in a co-pending application of Wayne E. Apuli, Serial Number 432,063 filed May 24, 1954 for Pelletizing Process now Patent 2,805,141 dated September 3, 1957.

It is desirable that the fuel coating on the pellets be of a uniform and predeterminable thickness for greatest efliciency in the induration process. Consistent operation of the pelletizing furnace as a continuous, day-byday and month-by-month process is dependent on such uniformity and such uniform thickness. A balling drum does not normally produce a uniform quantity of balls over any given period of time, either as to number, size, or total weight, and it has been quite difficult to attempt to supply to the coating drum the proper amount of powdered carbonaceous fuel to provide optimum coating conditions to produce a coating of uniform thickness. Those skilled in the art are now familiar with a method of determining quantitatively the amount of a magnetic material being carried past a sensing point, said method comprising providing a primary-secondary inductive couple consisting of a primary induction coil and one or more secondary coils, the couple being disposed adjacent to or surrounding the pathway, such as an endless conveyor or a pipe, along which the magnetic material is moved. When the primary is suitably energized, usually by an alternating current, a responsive current is induced in the secondary or secondaries. If then a magnetic material is conveyed past the inductive couple and closely adjacent thereto, the magnetic material will cause an intensification in the flux field, and the secondary current will be increased, and will be subject to fluctuations corresponding not only to variations in the primary current but also to variations in the amount of the magnetic material being conveyed past or through the coils as aforesaid. This varying secondary current can be measured and recorded to be accurately interpreted in units directly translatable into units of weight of the magnetic material.

Unfortunately several serious difiiculties beset the operator who attempts to supply to the coating drum an amount of powdered fuel based on the weight of concentrate being fed to the balling drum. The pellets discharged from a balling drum are neither uniform in size, nor in number, not in weight. Obviously if the carbonaceous fuel is supplied to the coating drum in a uniform manner by a conveyor responsive to the amount of concentrate fed to the balling drum, then there will be fed to the coating drum a uniform supply of fuel and a non-uniform supply of pellets. It might at first appear that the quantity of pellets issuing from the balling drum could be sensed continuously by an induction couple such as above mentioned, and that means could then be provided for continuously supplying the powdered fuel, this means being continuously responsive and correlated to the quantity, and variation in quantity, of the pellets under the control of the developed secondary current. Unfortunately this method is beset by practical difficulties mainly for the reason that the fuel conveyor, even though its speed may be accurately controlled, does not receive a continuously uniform supply of fuel on a weight-time basis. Normally the powdered fuel is fed to a conveyor from a hopper over an intermediate table feeder which, by suitable movements (either oscillatory or rotary, and usually under the additional influence of vibratory means), promotes, or is intended to promote, a fairly even supply of fuel to the conveyor. Nevertheless it has been found in the past that it was practically impossible to control accurately the supply of powdered fuel responsive to the varying quantity of pellets being carried past the sensing means.

We have found that it is first necessary to continuously sense and measure accurately the moment-to-moment variations of pellet weight on the pellet conveyor appreaching the coating drum, and, concurrently, not only to cause the fuel conveyor speed to vary proportionally to the sensed variations in the pellet supply but also to positively assure, by fuel feed control at the point of delivery to the fuel conveyor, that the proper quantity of powdered coating fuel is being supplied, under continuous and accurate control, to the fuel conveyor. Only in this way can the pellet quantity and the fuel quantity 2} be supplied synchronously and comlnensurately to the coating drum.

As may be determined from what has been said so far, the principal object of the present invention is to continuously measure the equivalent dry component of green pellets being delivered from a balling means, and to supply this quantity of pellets to a coating means simultaneously with the exact quantity of powered fuel necessary for proper operation of the subsequent indurating means.

A further object of our invention is to provide a means which insures that each pellet receives its proper quantity of coating material.

Another object of this invention is to provide a means of easily changing the proportion of coating material to pellets, which ratio, being once established, will be automatically continued without operators attention.

Still another object of the invention is to develop a system in which the proper quantity of coating material will be available for the delivered quantity of pellets, irrespective of variations in the quantity of pellets being delivered, and irrespective of the feeding characteristics of the coating material, be it erratic or uniform.

It will be understood that the principles of the inven tion are equally applicable to the automatic proportioning of a second material to a first material while both are being delivered to an operating zone, as long as said first material has magnetic characteristics capable of effecting a coupling between primary and secondary coils in an inductive couple. It will be further understood that in the embodiment of the invention to be herein described and illustrated, the operation of adding coal dust to ore pellets has been selected for convenience of exemplification, and as one definite embodiment of a useful application of the invention.

In the drawings:

Fig. 1 is a schematic showing of our automatic material proportioning system.

Fig. 2 is an electrical wiring diagram showing the operative relationship of the various electrical elements of the system.

Figs. 3, 4 and 5 are more detailed circuit diagrams of particular control elements of the system.

Referring first to Fig. l, moist pellets are formed in balling drum and are discharged on endless conveyor 21 which may be of a trough type having a floor and side walls. In this instance the conveyor passes in succession through three annular coils constituting an inductive couple consisting of a primary coil P which is disposed between a pair of appropriately connected secondary coils S and S These coils are arranged coaxially to permit passage of the conveyor therethrough, and variations in the amount of magnetic material on the conveyor are reflected in variations in secondary coil current in the circuit to recorder 22. Conveyor 21 is driven at a constant speed by motor 23. Since the percentage of magnetic material in the pellets is uniform, the secondary current to recorder 22 is directly proportional to the actual tonnage of pellets travelling on conveyor 21. This is recorded as dry tons of concentrate on recorder 22. Recorder 22 transmits to ratio controller 23 a signal the strength of which is proportional to the aforesaid secondary current from coils S and S Simultaneously with the procedure so far described, a carbonaceous fuel such as powdered coal dust is delivered from hopper 24 to conveyor 25 and this coal dust proceeds to the left (Fig. 1) until discharged into a chute 26 along with pellets from conveyor 21. The mixture of pellets and coal dust proceeds to a coating drum, not shown. The coal conveyor is driven by a variable speed motor 27, and this motor 27 likewise drives a tachometer generator 28 the output of which is of course a current which pulsates in response to speed variations in motor 27, so as to reflect speed variations of coal conveyor 25. The output from tachometer generator 28 is fed as a signal to ratio controller 23 to be there combined with the signal from recorder 22 to indicate a preliminary relationship between the speed of the coal conveyor 25 and the amount of concentrate.

In Fig. 1 the lines extending between various control rectangles and the motors or other operating elements indicate that electric circuit elements are present (as will later appear) to operatively connect the said controls and operating elements, and the arrows beside said lines indicate the direction of energy transmission.

Ratio controller 23, through output circuit 29 imposes a speed variation control on coal conveyor motor 27, and simultaneously the said ratio controller 23, through output circuit 30, imposes a corresponding and commensurate speed control on motor 33 which operates feeder table 34. As previously indicated, feeder table 34 may operate subject to several types of applied movement. It may rotate and simultaneously vibrate, all responsive to motor 33.

So far we have seen that coal conveyor 25 and coal table feeder 34 are each responsive to signals from ratio controller 23 which in turn is operatively responsive to secondary current changes in the current from secondary coils S S when changes occur in the content of magnetic material moving on conveyor 21. Nevertheless, as we have already explained, this does not satisfactorily solve the problem because conveyor 21 and table feeder 34 may respond perfectly to signals from ratio controller 23, and yet coal delivery to conveyor 25 might even be stopped altogether, so that the end result would be entirely unsatisfactory. We have solved this problem by imposing on table feeder motor 33 a trimming control which corrects for inadequacies in coal delivery from the feeder tab-1e. This correction is fool-proof and positive because it responds directly to the actual weight of coal delivered to coal conveyor 25. This is accomplished as follows.

We have provided a scale head which responds accurately to the weight of coal on a measured length of coal conveyor 25. Still referring to Fig. 1 it will be noted that conveyor 25 is of the endless type, and its upper or load-bearing flight is supported on spaced rollers or rods 35 extending transversely under the conveyor belt. The weighing zone extends between the two rollers 35a, 35b. At the mid point between rollers 35a, 35b, the belt runs in contact with a weighing mechanism comprising the vertically movable arm 36 to which is pivotally connected a lever 37 and this in turn is pivoted in a bearing 38 on the machine frame. This lever 37 is in operative contact with a load cell 40, the operation of which will be later explained in more detail in the description of the main wiring diagram, Fig. 2. Suffice it to say here that the load cell develops and transmits to a recorder 41, a proportional timer 42a, and a motor 42 a signal which is then routed to table feeder motor 33 through circuit 43. This revises in the desired direction, the speed of motor 33.

As a brief resume, if the induction couple reports to recorder 22 and ratio controller 23 that the weight of pellets is increasing on conveyor 21, and if ratio controller 23 correspondingly increases the speed of coal conveyor 25 and table feeder 34, the scale head mechanism may report and record the fact that the coal weight arriving on conveyor 25 is inadequate to meet the situation. This might happen if the coal powder is sticky with moisture, and is blocking the feeding path. The scale head signal will activate recorder-controller 41 and consequently will immediately im the speed of table feeder motor 33, in the assumed example by increasing the agitation movement of the table feeder 34. This insistent demand will continue, and if necessary will increase, until the scale head mechanism impresses on the load cell the fact that the coal supply is adequate. The reverse of the above operation will be produced if the feed becomes too free, and an overweight of coal reaches the weighingzone.

assaoae For purposes of inventory the total amount of. coal supplied to the pellets can be registered in an integrating mechanism 44 which receives from the scale head a signal directly proportional to the weight of coal on a unit length of belt. This figure is integrated with a second signal the intensity of which is proportional to the rate of travel of conveyor 25, the resultant being calibrated to be directly readable in tons per time unit.

By means of the system thus described the delivery of coal to the pellet coating drum is accurately proportioned to the pellets arriving from the balling drum.

Referring now to the electrical circuits and members associated therewith we show, in the upper left portion of Fig. 2, the sensing means for quantitatively determining the amount of magnetic material moving in a path past an induction couple consisting of primary coil P and two secondary coils S and S which in a structural assembly are axially spaced one on each side of the primary. The conveyor 21 (Fig. 1) passes through the couple, and any magnetic material thereon increases the induced current in S S An A.C. current from L L feeds into a constant voltage transformer 50 through a resistor 51 into primary P. One side is grounded at 52. The voltage developed in S S is proportional to the quantity of magnetic material on the conveyor.

The A.C. current flowing in the secondary circuit is rectified by diode 53 so that the DC. voltage drop across resistor 54 is proportional to the aforesaid amount of magnetic material. It is necessary to make an operating correction for extraneous effects in the operating circuit other than those resulting fom passage of the magnetic concentrate on the conveyor. This correction is effected by taking part of the transformer output through a phasing capacitance 55 and a variable resistor 56 in conjunction with a fixed resistor 57. In essence, the object is to vary resistor 56 to produce at diode rectifier 58 a Volt age equivalent to that at diode 53 when the circuits are energized but no magnetic material is passing on the conveyor. Under these conditions the DC. voltage across resistor 54 is equal and opposite to the D.C. balancing voltage across resistor 59 with no magnetic material passing:

A variable resistor 62 and a coupled capacitor 63 act as a matched resistance-capacitance circuit to dampen the signal developed by passage of magnetic material. Resistor 62 could be of fixed value, but for convenience a variable resistor is provided to modify the signal voltage at points 64, 65, so that a signal of predetermined potential can be fed to the subsequent circuit elements.

The signal from points 64, 65 is shown in Fig. 2 as being delivered in succession to two units, in this drawing identified by reference numerals 22a and 22b and consisting respectively of a. measuring circuit and an amplifier, these items being incorporated in the block marked 22 in Fig. 1. The measuring circuit is shown in greater detail in Fig. 3 and a suitable amplifier in Fig. 4.

Referring now to Fig. 3, the points 64 and 65 on Fig. 2 may be indicated as the input points similarly identified at the bottom of Fig. 3. In the circuit of Fig. 3, as will directly appear we have provided a battery-balanced resistance bridge. The battery is periodically checked against a commercially obtainable laboratory standard cell which, when used only as an occasional check means, remains at constant value for a long period. We have provided a multiple throw switch 68 which can be manually thrown to a check position at selected intervals, but which normally is in the opposite or running position.

At the signal input point there is a resistor-capacitor alternating circuit consisting of resistor 69 and a capacitor 70. Switch 68 is in the upper or normal operating position, which places resistor 69 in electric circuit communication with point 71 through lines 72 and 73. The upper part of Fig. 3 constitutes a balancing bridge of the Wheatstone general type, in which points 74, 71, 75 and the intermediate resistors 76 and 77 form a lower arm,

and points 74, 78, 79 and 75 and the intermediate resistors 80, 81, and the parallel resistor assembly 82, 83 and 84 form the upper arm. The intermediate cross arm 74, 85, 75 contains the battery 86 and a variable resistor 87. In the parallel resistor bank 82, 83, 84 is a variable element for balancing purposes.

Battery 86 supplies a constant voltage between points '74 and 75. This voltage is arranged to be of opposite polarity to the signal being measured. With the switch still in the upper position the incoming signal to be measured proceeds from point 64 through lines 72 and 73 to point 71, and from point 65 through the amplifier (connected at points 90 and 91) and then through lines 92 and 93 to point 60. Signal voltage at the terminal points 71 and. 60 therefore is disposed, by means of the measuring bridge above described, to be opposed in polarity to the voltage of battery 86. The amplifier in series with terminals 90 and 91 is connected to measure and amplify any dilference between the established battery voltage and the fluctuations in the incoming signal from the induction couple heretofore described. The amplified current energizes a motor 94 (Fig. 2) which in turn operates a number of items, as will appear. It may now -'be stated that one of its functions is to operate the sliding contact on resistor 84 (Fig. 3) to a position such that the voltage produced by battery 86 across points 71 and 90 is equal and opposite to the incoming signal at 64, 65. It is apparent that when the signal is thus'balanced there will be no output signal at points 90 and 91, which will in turn leave no potential to be amplified and consequently motor 94 (Fig. 2) will stop. Motion of the motor to the stop position, however, will have made the necessary adjustments in the further controlled elements to achieve the preliminary results desired.

To assure a proper balancing voltage output from battery 86 (Fig. 3) it is occasionally checked against a standard cell 95, as follows. Manual switch 68 is moved to its checking position, during which movement a clutch mechanism (not shown) simultaneously connects the slider on resistor 87 with motor 94 (Fig. 2).

With the switch in the down or check position the voltage originating in battery 86 and developed across resistor 77 is compared with the voltage of standard cell 95 and impressed between points 96 and 97. Since the signal voltage at terminals 64- and 65 has been disconnected by moving switch 68 to the check position, the amplifier will now amplify a differential impressed across resistor 98, the amplifier circuit proceeding from terminal 90 through lines 92, 100, resistor 98, lines 101 and 102 to terminal 91. Any detectable potential difference between the battery 86 and standard cell 95 will be amplified by the amplifier which will cause motor 94 to move and to operate the sliding contact on variable resistor 87 so as to cause the battery voltage across resistor 77 to balance the standard cell voltage 'by making the two voltages equal and opposite. This will periodically check and adjust the battery voltage and insure accurate measuring of the incoming signal at 64, 65. Switch 68 is of course returned to the upper or normal operating position after each check.

In this measuring circuit, Fig. 3, no reference has as yet been made to resistor 105. This resistor, by means of the fixed terminal point 106 and the movable terminal point 197 will be later referred to. Briefly this variable resistor provides a potential drop arrangement which is used as a supply of constant voltage, low wattage power for a retransmitting slidewire unit.

Proceeding from terminal points 90 and 91 of Fig. 3 we arrive at the similarly identified terminal points at the left side of the amplifier diagram, Fig. 4. This shows a fairly conventional D.C. amplifier which takes the low potential signal coming in at 90, 91 and amplifies it sufficiently to energize balancing motor 94 (Fig. 2). As has been seen, the balancing motor operates to return the energizing voltage to a zero value. As heretofore intilmated, as long as the voltage at terminals 64, 65 is constant no potential difference is detected at terminals 90, 91. The position to which motor 94 moves to achieve this balance is then representative of the signal impressed at the points 64, 65. The motor 94 operates a pen, schematically indicated by a rectangle 108 on Fig. 2, which records the value of the signal voltage.

In Fig. 4 the unbalance of the measuring circuit is noted at terminal points 90 and 91 and is converted to alternating current by input transformer 109 and converter 110 and shaped by the matched resistor-capacitor elements 111 and 112. The alternating current signal is then fed to two 12AU7 tubes 113 and 114 in tandem amplifying relationship, and thereafter the output from tubes 113 and 114 is delivered to the grids of two l2AX7 tubes 115 and 116. The greatly amplified signal is then fed to one winding 94a of the split phase motor 94 already mentioned (Fig. 2) the other winding 94b being energized from lines L3 and L4 of a 110 volt A.C. supply. Power transformer 117 has a primary 118 energized from lines L3, L4 with an optional adjustable tap 1180. Various secondary taps provide voltages where needed, for ex ample taps 119 and 120 supply plate potentials of approximately 275 volts for the tubes 115 and 116, and taps 121 and 122 supply filament voltage for tubes 113 and 114. Since the amplifiers characteristics and circuits will be apparent to one skilled in the art, no further or more detailed description is necessary.

Summing up at this point the functions of motor 94, which responds to amplifier 22b shown in block outline in Fig. 2 and in circuit detail in Fig. 4, the motor operates (a) a pen for recording (b) the moving slider on battery rheostat 87 (Fig. 3), (c) the sliding connector on rheo stat 84 (Fig. 3), (d) a retransmitting slidewire connector on rheostat 23 (Fig. 2), and (e) an auxiliary switch cam to operate a switch 124 (Fig. 2). The last two functions will be explained hereinafter. Terminals 106 and 107 already referred to as a source of constant voltage on Fig. 3 may now be again identified at the top right of Fig. 2 by means of the same reference numerals.

We have now rather fully explained the development of an electrical signal proportional to the amount of magnetic material travelling on a conveyor towards a coating drum, and the rendering of said signal operative on a motor 94 to perform certain further operations. We will now proceed to a description of the means whereby the amount of powdered coal is controlled so as to be fed to the coating drum in proper proportion to the amount of magnetic pellets entering the coating drum.

Referring again to Fig. 2, a signal comprising a potential drop from terminal points 106 and 107 (Fig. 3) is applied at the same points at the top right of Fig. 2 and is rendered effective on retransmitting slide wire resistor 123 through dropping resistor 126 and lines 127 and 128 to two points 129 and 130 of an electric bridge 124. Two opposed points 131 and 132 on the same bridge receive, through lines 133 and 134, a signal from tachometer generator 28. This signal passes through dropping resistor 136 and voltage divider 137, the signal being proportional to the coal being mixed with the pellets. The signal is attenuated by the matched resistor 138 and capacitor 139, and the amplifier 140 and motor 141 are connected in the circuit similar to the previous connection of amplifier 22b and motor 94 in the pellet signal circuit. It should be noted that the tachometer generator 28 emits a signal which is proportional to the increment of length of belt passing a point in a unit of time.

If there is any difference between the two voltages fed to electric bridge 124, which are opposite in polarity (one from pellet weight and one from coal weight) the difference will be detected and amplified by amplifier 140 and will cause motor 141 to operate in an equalizing direction. The motor moves the slidewire at bridge point 132 until the bridge 124 again shows a zero balance. The motor position is therefore an indicator as to the ratio of coal to pellets.

In moving to the balancing position motor 141 also moves the slider on a control slidewire 144 which is in circuit in an electroline relay 145 (to be explained in connection with Fig. 5). Mechanically the slider at 144 is at midpoint when motor 141 is at a predetermined and preset position. The relay is arranged so that When slider 144 moves from center the relay transmits a signal to modutrol motor 146 which operates a sliding contact on potentiometer 147 so as to change the speed of coal conveyor motor 27. It will be understood that potentiometer 147 is operatively wired in the field circuit of motor 27. This change of speed of conveyor 25 of course changes the signal produced by tachometer generator 28, which change is detected by amplifier 140, and the amplifier transmits to motor 141 a signal which causes it to operate the sliders at 132 and 144 as aforesaid, and as shown in broken lines on Fig. 2. This will again balance the circuit and return the sliding point 144 to its preset position.

The assembly comprising the control slidewire 147 and associated electrical operating elements effective on motor 27 are shown more fully in Fig. 5. This is a. standard relay obtainable commercially, and manufactured at the present time by Minneapolis-Honeywell Regulator Company. The purpose of this relay is to accept a signal from the slidewire contact 144 and, responsive thereto, to produce a signal effective on motor 27. This operation involves control of proportional band, reset, and approach rate functions which are familiar to those skilled in the motor control art. It is not necessary to go into extended detail as to the manner of operation of the electroline relay control of a modutrol motor beyond the brief characterization following.

Fig. 5 shows the control for modutrol motor 27. A signal entering at terminals 151 and 152 becomes effective, through the various proportional band resistors 153, 154, 155, 156, 157 upon tube 158, the output of which is fed to tubes 159. There are interrelated modifying effects produced by heaters 160 and 161 in conjunction with electrical bridge 162, and the resultant signal is imposed on tubes 163 and 164. The ultimate effect, through the media of relay coils 165 or 166 operates contacts 167 or 168 respectively, and consequently controls the rotat'ion of motor 27.

We have so far described in detail the automatic control of the coal belt conveyor 25 responsive to the amount of magnetic material on conveyor 21, and we have described a trimming effect on the coal table feeder responsive to actual amount of coal on belt 25 as determined by a scale head effective on a load cell in block 40, Fig. 1.

Briefly reviewing, the percent carbonaceous fuel, in this case coal dust, is based on the maintenance of a constant weight per foot on the conveyor 25. This involves effective control of the speed of table feeder 34. This speed is responsive to a main control, from ratio controller 23 (Fig. 1) and a trim control, responsive to a load cell 40, which is more specifically shown in Fig. 2 in its circuit detail. The main control involves the simultaneous control of potentiometer sliders at 147 and 171, Fig. 2, each responsive to motor 146, and respectively controlling the speeds of motors 27 and 33, namely the coal conveyor motor and the table feeder motor. Since the output of a table feeder, even when controlled as above, is not uniformly proportional to table speed, a trim control is needed, responsive to the actual weight of coal per unit length of the conveyor 25. This operates as follows.

Transformer 172 receives an AC. line voltage supply from L5 and L6 which is converted to DC. in rectifier 173 and then attenuated by the hookup consisting of resistor 174 and the parallel capacitors 175 and 176. The resultant rectified current is fed to opposite end points 177 and 178 of a load cell 40 through compensating resistors 179 and 180. It will be understood that the electrical characteristics, including the resistance, of a load decades 9 cell varies with tension or compression applied on operative points thereon and the purpose of the scale head structure, previously described as in contact with a fixed length of coal conveyor, is to apply to the load cell varia-" tions in tension or compression. These variations will be directly responsive to variations in actual coal weighton the conveyor belt span being sensed, and will cause cor responding variations in the load cell electrical balance. Variations in load cell balance will be effective at bridge points 183 and 184.

Points 185, 186, 187 and 188 provide reference points for an electrical balancing bridge, with a constant voltage being supplied across points 186 and 187. This develops a voltage across points 188 and 185 which is opposite in polarity to the voltage from points 183 and 184 on the load cell. Any inequality in voltage is detected by amplifier 189 which in turn will appropriately operate trimming motor 41 to operate the slider on resistor 187 to return the electric bridge to a balance point. The motor position is a measure of the load on the belt.

Motor 41 has additional functions. It is effective to close either a switch 190 or 191 upon appropriate rotative movement of the motor. The operative linkage is not here shown, but the motor can rotate a cam which will close either switch 190 or 191 depending on the direction of cam movement. The cam can be set at a midpont representing a preset valve of weight per unit of conveyor length. Closure of either switch 190 or 191 operates motor 42 through appropriate intermittent timing means 42a, the motor and its timer being energized from line terminals L7 and L8. Motor 42, when energized, operates a slider on motor potentiometer 193 which has a trimming effect on table feeder motor 33.

It will be recalled that table feeder motor 33 is also responsive to the operation of another potentiometer 171 which is actuated by motor 27.

It is desirable to record the total weight of coal supplied to the pellets. This is accomplished by detenmining the coal conveyor speed and multiplying it by the weight per unit of length. The results are recorded on recorder 44 (Fig. 1). Referring again to Fig. 2, tachometer generator 28 produces a voltage proportional to the speed of the coal conveyor 25 and feeds this voltage to a resistance bridge at operating points 194, 195, 196 and 197. As previously noted motor 41 (responsive to load cell 40) has a number of functions, and one of those functions is to move a sliding contact at point 197. This movement is of course responsive to change of coal weight on belt 25 (Fig. 1). The output across the bridge is measured at points 196 and 197, transmitted to a measuring circuit 198 and amplifying circuit 199 identical with those already respectively shown in Figs. 3 and 4 and the amplifier output is imposed on motor 200 which appropriately moves to record and show the total weight of coal.

What is claimed is:

1. Apparatus of the character described for automatically proportioning the relative amounts of a first material and a second material when said materials are moving in a continuous process, and when said first material has magnetic characteristics, said apparatus comprising a first conveyor for receiving said first material and moving it past a measuring zone, sensing means at said measuring zone responsive to variations in quantity of said magnetic material, a ratio controller, means establishing an operative connection between said sensing means and said ratio controller whereby said ratio controller receives a first signal proportional to the amount of magnetic material passing said sensing means, a second conveyor for receiving said second material, driving means for said second conveyor, a tachometer, means operatively linking said tachometer with said second conveyor whereby said tachometer is responsive to rate of movement thereof, means operatively connecting said tachometer and said ratio controller whereby to transmit to saidratio controller a second signal proportional to the rate of movement of said second conveyor, balancing means operatively associated with said ratio controller for comparing said first and second signals, said balancing means being operatively linked with and effective upon said driving means for said second conveyor whereby to control the rate of movement of said second conveyor proportionally to variations in the amount of said mag netic material passing said sensing means on said first conveyor.

2. Apparatus as defined in claim 1 wherein said sensing means comprises an inductive couple consisting of primary and secondary windings said primary winding being energized from a source of electric power, and the induced current in said secondary winding being ope-ratively applied to said ratio controller.

3. Apparatus as defined in claim 1 wherein said tachometer includes an electrical generator connected to vary its output responsive to variations in the rate of speed of said second conveyor, and electric circuit means establishing an operative connection between said generator and said ratio controller.

4. Apparatus as defined in claim 1 including, in combination' therewith, a material feeder associated with said second conveyor and adapted to discharge said second material on to said second conveyor, feeder energizing means for operating said material feeder, and means operatively linking said ratio controller and said feeder energizing means whereby operation of said material feeder is proportionally aifected by variations in said first signal.

5. Apparatus of the character described for automatically proportioning the relative amounts of a first material and a second material when said materials are moving in a continuous process and when said first material has magnetic characteristics, said apparatus comprising a first conveyor for receiving said first material and moving it past a measuring zone, sensing means at said measuring zone responsive to variations in quantity of said magnetic material, a ratio controller, means establishing an operative connection between said sensing means and said ratio controller whereby said ratio controller receives a first signal proportional to the amount of magnetic material passing said sensing means, a second conveyor for receiving said second material, driving means for said second conveyor, a tachometer, means operatively linking said tachometer with said second conveyor whereby said tachometer is responsive to the rate of movement of said second conveyor, means operatively connecting said tachometer with said ratio controller whereby to transmit to said ratio controller a second signal proportional to the rate of movement of said second conveyor, balancing means operatively associated with said ratio controller for comparing said first and second signals, said balancing means being operatively linked with and effective upon said driving means for said second conveyor whereby to control the rate of movement of said second conveyor responsive to variations in the amount of said magnetic material passing said sensing means, a material feeder associated with said second conveyor and adapted to discharge said second material on to said second conveyor, feeder energizing means for operating said material feeder, means operatively linking said ratio controller and said material feeder whereby operation of said material feeder is proportionally affected by variations in said first signal, a scale in operative contact with a material-carrying span of said second conveyor whereby to measure the actual Weight of said second material passing said span, means operatively linking said scale and said feeder energizing means whereby to impose on said feeder energizing means a trim control simultaneously with the control exercised thereon by said ratio controller.

6. Apparatus as defined in claim 5 wherein said scale is provided with an associated electrical load cell, the

131 output of which varies proportionally With variations in Weight imposed thereon by said scale, and electrical circuit means operatively linking said load cell and said material feeder energizing means.

7. Apparatus as defined in claim wherein said sensing means comprises an inductive couple consisting of primary and secondary windings, said primary winding being energized from a source of electric power, and the induced current in said secondary winding being operatively applied to said ratio controller.

8. Apparatus as defined in claim 5 wherein said tachometer includes an electric generator connected to vary its output responsive to variations in the rate of speed of said second conveyor, and electric circuit means establishing an operative connection between said generator and said ratio controller.

9. Apparatus as defined in claim 7 wherein said primary and secondary windings surround said first conveyor.

10. Apparatus of the character described comprising a receptacle for receiving magnetic pellets and pellet coating material, a first conveyor for delivering said pellets to said receptacle, a sensing means adjacent said first conveyor and adapted to produce a signal responsive to the quantity of pellets passing on said first conveyor, a ratio controller in operative association with said sensing means whereby to indicate such quantity, a second conveyor for carrying said coating material to said receptacle, driving means and speed control means for said second conveyor, feed control means for varying the amount of coating material delivered to said second conveyor, electric circuit means operatively linking said ratio control means with said sensing means, a second electric circuit means operatively linking said ratio control means with said speed control means and with said feed control means, whereby to vary both the rate of movement of said second conveyor and the rate of coating material discharge on said second conveyor proportionally to each other, and responsive to variations in the quantity of pellet material travelling on said first conveyor.

11. Apparatus as defined in claim 10 wherein there is provided, in combination with said apparatus, a second sensing means adjacent said second conveyor and responsive to coating material weight per increment length of conveyor, an electric load cell in association with said second sensing means and having an electric current output proportionally varying with said weight per unit length, and a third electric circuit means carrying to said feed control means a signal proportional to said electric current output from said load cell, whereby to integrate at said feed control means the controlling influence of said ratio controller and said load cell.

References Cited in the file of this patent UNITED STATES PATENTS 1,730,893 Lechtenberg Oct. 8, 1929 2,150,440 Hargreaves Mar. 14, 1939 2,207,327 Maurer July 9, 1940 2,280,656 McCoy Apr. 21, 1942 2,727,733 Carswell Dec. 20, 1955 FOREIGN PATENTS 607,821 Great Britain Sept. 6, 1948 

